Air bag devices are commonly provided in a vehicle as a safety device for occupant protection that protects an occupant from impact upon vehicle collision. Conventionally, in order to prevent gas released from an inflator from leaking from the bag, fabric coated with a resin material was mainly used, but fabric needs to be light in weight due to demands for improvements in fuel consumption and the like and needs to be compactly housed due to trends in steering wheel design and the like, and thus non-coated cloth has been widely adopted.
Also, an air bag made of nylon 66 (PA66) was mainstream, but an air bag made of polyethylene terephthalate (PET) is beginning to be adopted for the purpose of reducing cost.
However, there is the issue that polyethylene terephthalate having a higher modulus than nylon 66 has poor foldability. Also, there is the issue that a gap tends to form in the thickness direction between weaving threads due to a high modulus, and low gas permeability is unlikely to be achieved.
To address these issues, Patent Literature 1 discloses a technique regarding a non-coated fabric for an air bag that exhibits excellent storability and expansion responsiveness and in which the fineness of filaments constituting the fabric, the single fiber fineness of filaments, the amount of fibers per unit area, gas permeability, thickness, and a bending resistance measured using a cantilever method are defined. However, the non-coated fabric for an air bag obtained by this technique has a gas permeability of 0.5 to 3.0 ml/cm2·sec obtained using a Frazier method (0.9 ml/cm2·sec or more obtained using a Frazier method in working examples), which cannot be considered as having low gas permeability, and thus is not sufficient in terms of performance as a fabric for an air bag.
Also, Patent Literature 2 discloses a technique by which a flexible fabric that has little fuzz and thread breakage, foldability, and low gas permeability is obtained by forming a fiber structure using a composite fiber yarn obtained using sea-island composite spun yarn and then forming extremely fine fibers using the fiber structure. However, the gas permeability of the fabric obtained using this technique cannot be considered as being low (0.7 ml/cm2·sec or more obtained using a Frazier method in working examples), and the cost of the raw yarn is high due to a sea-island composite yarn being used as the raw yarn, and the manufacturing cost is also high due to the need for processing to remove the sea component. Furthermore, there is a possibility that flame retardancy will decrease if processing to remove the sea component is insufficient, and thus this fabric is not suitable as a fabric for an air bag.